Data management platform. (the words mean more than the literal meaning btw)

Imagine you have some customer records with customer identifiers. You want to map those to data that others hold on your customers to get a better understanding of your customer's "habits". You need a DMP to map your data to the 3rd party data and it needs to be done in a way such that its not processing identifiable data, as its certainly likely to be outside the usage your customer agreed to. DLS talked about using a hash (random number) to replace the identifiable index with an non-identifiable index. That is the same concept that exists in a DMP.

And also a payment card hub for example (credit card data)

If you are wondering why these exist its because with only one player in the search business - there has been a bidding war of people competing for search terms.

Rumour has it that "car insurance" often retails for $10 a click. So if you are britains biggest car insurer with (and I made this up) 15M customers, you probably don't want to be paying $10 a click when you have a 1 : 2 chance of paying to market an existing customer.